Materials for facade decoration – comparison and selection criteria

Traditionally facades were decorated with the creation of profile elements (cornices, string cornices, architraves etc.) by means of the pulling method of wet plaster mix moving a pattern on guides directly on a facade, above bonder lines of bricks overhanging flat wall area, which are established in a project and cut in size of a future profile during brick laying. Non-core elements were made by casting method from stucco.
This method demands long-term behavior of qualified plasterers in difficult weather conditions and height. Industrial production of ready facade decoration elements and their subsequent installation allow to decorate a building faster, cheaper and with predicted quality.
At present time in construction it is used facade decorative products made of concrete, flexible foam and expanded polystyrene.
Concrete is a mix of cement, mineral dust, polymeric additives and fibres, products from which are molded according to the following technologies:
- architectural concrete is a vibrocompression of a moist cement mix, sand and softeners in rigid moldings.
- fibre-concrete is a molding formation of concrete mix with addition of polymeric or fiber glasses up to 5 %.
- glass-fiber reinforced concrete is a spraying of modified cement-sand mix with simultaneous submission of glass fiber up to 10 % in this mix on molding surfaces with reception of thin-walled products (12-15mm).

Polyurethane foam is formed in a closed molding under pressure
Expanded polystyrene – profile elements are cut out from a sheet material by means of heated stretched string in the machine tool with CPU. The further processing of the surface is possible by the following methods:
- pasting of fibreglass mesh and manual overcoating with materials according to the system of "wet" facade directly on a building site.
- covering with acrylic mix with mineral dust (sand, marble crumb) in industrial conditions.
- covering with a special polymer-impregnated concrete mix in 2 layers in industrial conditions.

Products, made according to the listed above technologies, have both the advantages and the certain disadvantages depending on requirements to facade elements.
Size: hollow construction from glass-fiber reinforced concrete (and sometimes fibreglass) can be applied to products of large size, for example, cornices with carrying out more than meter, which, however, demand complex substructure for fastening to a wall.
Cast concrete products of large sizes are too heavy for manual installation and it is necessary to crush a profile in short sections with a big number of joints.
Although, lightweight products from expanded polystyrene and polyurethane foam are technologically limited in sizes, it is possible to collect a large profile from several parts. Durability of an element from light materials with big carrying out can be insufficient for keeping snow load that is solved by installation of outflow with a separate system of fastening to a wall above it.
Weight: Products from concrete essentially weigh giving additional load on walls and a basement. Moreover, modern facades systems* (so-called "wet" facades with a plaster layer on an insulant from expanded polystyrene or dense mineral cotton wool and also suspended ventilated facades) have little loading-carrying ability. Installation of heavy concrete elements on systems of light facades needs a construction carrying substructures. Elements from expanded polystyrene and polyurethane foam can be mounted due to glue with additional fixing of expansion bolts, but elements with little carrying out are only due to glue.
Complicated forms and the opportunity of manufacture of non-standard elements: products made by molding, vibrocompression or foaming in forms can have a difficult form with a decoration. Products made by moving a pattern on guides are only profile, however, it is possible to receive an additional decoration by imposing of plaster molding. Moreover, manufacturing of patterns is much cheaper than manufacturing of forms that gives an opportunity to manufacture of short runs of non-standard products.
Durability: Products based on cement mixes are sufficiently open-textured, they can be sated with moisture. Cycles of freezing – thawing leads to occurrence of hairline cracks and to gradual, though also rather slow (decades), destruction. It is recommended water-repellency treatment, painting, protection by means of drips, water drainage from a roof.
Expanded polystyrene and polyurethane foam without any covering collapse faster (less than year) under action of ultra-violet radiation of the sun. Products from polyurethane foam are protected only by a layer of the first coat and a paint. Mineral additives («quartzite of fine fraction», i.e. sand) in acrylic covering of polyurethane foam products also should protect acryl from the sun. The expanded polystyrene covered with a layer of polymer-impregnated concrete mix is reliably protected from ultraviolet.
Combustibility: concrete products are actually nonflammable, but steel carrying constructions lose carrying ability during heating in a flame of fire that could cause a collapse of heavy decorative elements.
Polyurethane foam and expanded polystyrene are combustible material, not without reason there are no fire certificates of manufacturers on their websites. At combustion of many polymeric materials it is typically that formation of hot melt drops promotes distribution of fire downwards on a facade and also high smoke generation.
Expanded polystyrene covered with polymer-impregnated concrete is certificated on class G1 (sickly combustible). At fire tests it is established that a part of expanded polystyrene burns out, but there is no formation of burning hot melt drops and burning out for all length of a sample..
Compatibility with systems of final finishing of facades: Decorative facade finishing stucco and facade paints are appreciably designed for the plaster cement base. Polymeric coverings of decoration elements are not always compatible with painting system of a facade plane, for example, it is impossible to use silicate paints for polyurethane foam.
Joints of elements: Joints of concrete elements are usually well visible, it is an inevitable feature of the technology and manufacturers do not think it is a defect. Polyurethane foam with exact geometry and strongly stuck together on end faces allows to create almost a monolithic structure in an interior, but different disturbance ratios of polyurethane foam and facade materials at temperature differences frequently lead to a divergence of joints. Expanded polystyrene covered with polymer-impregnated concrete observing the technology joints closing gives a homogeneous structure. Some complexities can arise with structures of small thickness (up to 25mm) – the product turns out fragile, but the area of expanded polystyrene in a joint becomes insufficient for pasting on fibreglass mesh. In this case an expanded polystyrene structure is covered directly on a facade.

* In the last decade in Russia the new regulations (in particular SNIP 23-02-2003) establishing higher parameters of facades thermal insulation were accepted. These norms have predetermined use of lightweight materials with high thermal insulation in facade decoration – mineral cotton wool and expanded polystyrene. Also it is widely used an aerated concrete and a large formatted porous brick in a low-rise building of a high price category. Thus, the most part of facades of new built and reconstructed buildings have small carrying capacity.